If you're on iOS:
Tap on the the watch you're no longer interested in receiving notifications for. In the example below, we'll remove a hotel watch:
After tapping on the flight or hotel, you'll be taken to watch details screen. Press the "Watching" button to toggle if off. You'll know that you've stopped watching a trip once it's advertising that you "Watch This Trip" again. 😊
If you're on Android (flights only):
Head to the "Watch" tab at the bottom of the app and tap on the three vertical dots next to the trip you'd like to stop watching.
From here, you can tap "Stop Watching This Trip" and you'll no longer receive notifications for that trip.